The classic experiment of Hakim and Higham [1]} is here important. They measured the refractive index increase in a dielectric fluid when located in the region between two plates in the presence of a strong electric field. Theoretical considerations of this effect can be found at various places; cf. [2]}, [3]}, [4]}, [5]}, [6]}. An interesting recent experimental confirmation of the dispersive effect is recently reported [7]}. These authors exploited the lack of axial symmetry in a single-mode optical fiber, and were able to measure the radiation force, including the electrostriction force, very accurately.
